I cloned `hologram-example` then ran `sudo gem install hologram` and these are the errors I got :(

hologram error

Building native extensions.  This could take a while...
ERROR:  Error installing hologram:
  ERROR: Failed to build gem native extension.

/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/bin/ruby extconf.rb
creating Makefile

make
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c autolink.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c buffer.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c houdini_href_e.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c houdini_html_e.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c html.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c html_smartypants.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c markdown.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c rc_markdown.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c rc_render.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
xcrun cc -I. -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/universal-darwin12.0 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -fno-common -arch i386 -arch x86_64 -g -Os -pipe -fno-common -DENABLE_DTRACE  -fno-common  -pipe -fno-common   -c stack.c
xcrun: Error: could not stat active Xcode path '/Developer'. (No such file or directory)
cc -arch i386 -arch x86_64 -pipe -bundle -undefined dynamic_lookup -o redcarpet.bundle autolink.o buffer.o houdini_href_e.o houdini_html_e.o html.o html_smartypants.o markdown.o rc_markdown.o rc_render.o stack.o -L. -L/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib -L. -arch i386 -arch x86_64     -lruby  -lpthread -ldl -lobjc  
i686-apple-darwin11-llvm-gcc-4.2: autolink.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: buffer.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: houdini_href_e.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: houdini_html_e.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: html.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: html_smartypants.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: markdown.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: rc_markdown.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: rc_render.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: stack.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: autolink.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: buffer.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: houdini_href_e.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: houdini_html_e.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: html.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: html_smartypants.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: markdown.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: rc_markdown.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: rc_render.o: No such file or directory
i686-apple-darwin11-llvm-gcc-4.2: stack.o: No such file or directory
lipo: can't figure out the architecture type of: /var/tmp//ccFdbTgk.out
make: *** [redcarpet.bundle] Error 1


Gem files will remain installed in /Library/Ruby/Gems/1.8/gems/redcarpet-2.2.2 for inspection.
Results logged to /Library/Ruby/Gems/1.8/gems/redcarpet-2.2.2/ext/redcarpet/gem_make.out

Hmm, I found this which seems related: http://stackoverflow.com/questions/11961032/xcrun-error-could-not-stat-active-xcode-path-volumes-xcode-xcode45-dp1-app-c

Do you have xcode and the command line tools installed?

@jcantrell-trulia Thank you!! Yeah I've got xcode and command line tools installed.

FYI this solution here works: http://stackoverflow.com/questions/11961032/xcrun-error-could-not-stat-active-xcode-path-volumes-xcode-xcode45-dp1-app-c